In physics, a ferrimagnetic material is one in which the magnetic moment of the atoms on different sublattices oppose as in antiferromagnetism but the opposing moments are unequal and a spontaneous magnetization remains. This happens when the sublattices consist of different materials or ions (such as Fe2+ and Fe3+).
Ferrimagnetic materials show no magnetic order above the Neel Temperature like antiferromagnets and can hold a spontaneous magnetization below it like ferromagnets. However, there is sometimes a temperature below the Neel temperature at which the two sublattices have equal moments, resulting in a net moment of zero, called the compensation point.
The oldest magnetic substance known is the ferrimagnet, magnetite, and it is among the materials that were classified as ferromagnets before Neel's discovery of ferrimagnetism and antiferromagnetism.
Shull's obituary, in which he is consistently called "Cliff," says that Shull confirmed antiferromagnetism in manganese oxide, presumably after 1938 (after the "war ended") and confirmed the Néel model for ferrimagnetism for magnetite, probably around 1950, as I interpret it.
Ferrimagnetic materials have magnetic atoms on two inequivalent sites, or two interpenetrating sublattices, with ferromagnetic interactions between atoms on the same sublattice and antiferromagnetic interactions between atoms on different sublattices.
Ferrimagnets exhibit a partial cancellation of moments in opposite directions, resulting in a net magnetization.
The magnetic behaviour of single crystals of ferrimagnetic materials may be attributed to the parallel alignment; the diluting effect of those atoms in the antiparallel arrangement keeps the magnetic strength of these materials generally less than that of purely ferromagnetic solids such as metallic iron.
Ferrimagnetism occurs chiefly in magnetic oxides known as ferrites.
The net ferrimagnetism is thus a complex result of antiparallel spin alignment among the three types...
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